HL-2203, Special Rept 2-92-002:on 920407,signal from Triaxial Time History Accelerometer Contained Excessive Amount of Noise & Instrument Declared Inoperable for More than 30 Days.Cause Not Determined.Root Cause Analysis Underway

Special Rept 2-92-002:on 920407,signal from Triaxial Time History Accelerometer Contained Excessive Amount of Noise & Instrument Declared Inoperable for More than 30 Days.Cause Not Determined.Root Cause Analysis Underway

ML20096D380
Person / Time
Site:	Hatch
Issue date:	05/11/1992
From:	Hairston W GEORGIA POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
2-92-002, 2-92-2, HL-2203, NUDOCS 9205180015
Download: ML20096D380 (5)

Text

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W. G Hairston, lH seno vu rme,t HL-2203 twe, owems 003382 May 11, 1992 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555 PLANT HATCH - UNIT 2 NRC DOCKE! $0-366 OPERATING LICENSE NPF-5 SPECIAL REPORT 2-92-002 SEISMIC MONITORING INSTRUMENT INOPERABLE FOR LONGER THAN 30 DAYS RESULTS IN SPECIAL-REPORT.

AS RE0VIRED BY TECHNICAL SPECIFICATIONS Gentlemen:

In accordance with the Unit 2 Technical Specifications section 3.3.6.2, Georgia Power Company is submitting the enclosed Special Re) ort concerning an event where a seismic monitoring instrument was inoperaale for longer than 30 days. This event occurred at Plant Hatch - Unit 2.

If you have any questions in this regard, please contact this office.

Sincerely,

/l/

W. G. Hairston, 111 JKB/cr

Enclosure:

Special Report 2-92-002 cc: (See next page.)

150070 Ugp i 9205180015 920511 PDR i l-U ADOCK 05000366 @:

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Geolgi;ll'onel a O.S. NJclear Regulatory Commission /

May ll, 1992 Page Two cc: Georaia Power Company Mr. H. L. Sumnor, General Manager - Nuclear Plant NORMS LS. Nuclear Reaulatory- Commili.igndshinaton._ D.C.

Mr. K. Jabbour, Licensing Project Manager - Hatch U.S. Nuclear Rea;1atory Commission. Reaion II Hr. S. D. Ebneter, Regional Administrator Mr. L. D. Wert, Senior Resident Inspector - Hatch ,

003382

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ENCLOSt!RE l

PLANT HATCH J UNIT 2 NRC DOCKET 50-366 i OPERATING LICENSE NPF-5 SPECIAL REPORT 2-92-002 SEISMIC MONITORING INSTRVtiENT INOPERABLE FOR LONGER THAN 30 DAYS RESULTS IN SPECIAL REPORT AS_R[QV I RED. SLIEC HN I C At. S P E C 1 F I C AT I QHS 3 A. REQUIREMENT FOR REPORT f This report is required mer Unit 2 Technical Specifications section 3.3.6.2. '

This section of the Tecinical Specifications states the seismic monitoring instrumentation shall be operable at all. times. Action statement "a": of ,

this section states that with one or more of the required seismic. monitoring ,

instruments inoperable for more than 30 days, a Special Re) ort is required ,

to be -submitted within the next 10 days -outlining t1e cause -of the +

malfunction and the plans for restoric the instrument to operable- status. .

In this event, seismic accelerometer 2L51-N004 was inoperable'for greater -

than 30 days; consequently, a Special Report is requited. ,

B. UNIT STATUS AT TIME OF EVENT-On 4/7/92,at approximately 1200 CST, Unit 2 was in the Run mode a't an '

a) proximately power level of 2436 CHWT (approximate 1y 100 percent rated tiermal power).

C. DESCRIPTION OF On 4/7/92, *' approximately 1200 CST, plant Instrument and-Control personnel.

were perfe eng plant procedure 575)!-L51-003-05, " Seismic Instrumentation

• Functional iest and- Calibration." -This -procedure is- required to. be 1 l performed semir.nnually by Technical Specifications Table 4.3.6.2-1. During- t performance of- the procedure,- the < signal from triaxial time-history' -

accelerometer 2L51-N004 was determined to contain~an excessive-amount of: i noise. - Therefore, .the -' seismic . instrument .was declared. inoperable and Limiting- Condition for Operation (LCO) 2-92-249 was initiated to track its-

, status. . Maintenance Work Order (MWO) 2-92-2103 was also initiated to investigate and correct the problem.

The instrument is- located inside: the drywell, .on a = carbon stec1' plate- '!

l - rigidly attached to the feedwater inlet line.to the Reactor Pressure Vessel.

! Since the drywell 1: inaccessible during power operation; and .since 'the unit . '

I was operating at power. repair-could not be effected before-the.30' day time -

limit expired. Consequently, on 5/7/92, PL51-N004 was stilicinoperable, and this Special Report.is required.-

- 003382 d

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ENCLOSURE (Continued)

SEISMIC MONITORING INSTRUMENT IN0PERABLE FOR LONGER THAN 30 DAYS RESULTS IN SPECIAl. REPORT AS RE0VIRED BY TECHNICAL SPECIFICATIONS D. CAUSE OF EVEN1 The root cause cannot be determined conclusively until access to the drywell can be attained and an investigation conducted.

E. ANALYSIS OF EVENT Four strong-motion triaxial time-history accelerometers are installed at appropriate location:; to enable prompt detemination of the severity of any earthquake which may be experienced. One of the instruments is installed in the switchyard to measure the- free-field-ground acceleration and functions es a sel,mic trigger. -Another is installed in the Diesel Generator bui'iding and the othar two accelerometers are located in- the Reactor Buildli.g: one on the east side of the Reactor Building drywell pedestal at elevation 87 feet, and the other inside the dryw 'l on a carbon steel plate rigidly attached to the feedwater inlet line to the Reactor Pressure Vessel. ,

The signals of the four accelerometers are. recorded on magnetic tape in the main control room. Following a seismic event, this data would be processed to compare the measured seismic response with the Unit 2 seismic design-basis.

In this event, the' accelerometer located on-the feedwater discharge'line was declared inoperable. However, the free-field accelerometer which functions as a seismic trigger and the other two accelerometers are operable and would provide sufficient data should'a seismic event occur. The accelerometers have no other design functions.

Based on the above information, it ie concluded that the event --has no adverse impact on nuclear safety. The above analysis is. applicable to all i operating conditions.

F. CORRECTIVE ACTIOdS Corrective actions.frr ;.h event include:-

]

1. Declaring seismic !.istrusent 2L51-N004 inoperable and establishing a tracking LCO.

2. Performing a root cause analysis and implementing. corrective actions as necessary ( i . e '. , completing MWO 2-92-2103) during the next Unit 2 l -- outage of sufficient duration where containment entry is to be maue.

! i, . . Returning 2L51-N004 to operable status during.the next Unit 2 outage of sufficient duration vhere containment entry is to.be made.

1 003382 L HL-2203 E-2_

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ENCLOSURE (Continued)

SEISMIC MONITORING INSTRUMENT IN0PERABLE'FOR LONGER THAN io DAYS RESULTS IN SPECIAL REPORT AS RE0VIRED BY TECHNICAL SPECIFICATIONS

4. A previous failure of seismic monitor 2L51-N004 occurred in 1990 and was reported by Special Report 2-90-002, dated March 26, 1990. The cause of the failure was determined to be vibration induced degradation resulting from the instrument's location on the reactor feedwater-piping. This instrument is a force-balance type accelerometer which-is sensitive to vibration. As a result of this failure, GPC performed an engineering evaluation of the _ feasibility of relocating 2L51-N004 and/or replacing the instrument to improve reliability. The evaluttion deternined relocation was not- desireable at' that time.

Discussions with the vendor were held concerning tiie need to increase the instrument's reliability. As a result, _ seismic monitor 2L51-N004 was replaced with a like kind instrument having an increased range.

However, as evidenced by the current component failure, the desired reliability has not been achieved.- Coasequently, seismic monitor 2L51-N004 will be replaced during each refueling outage until the desired reliability is obtained by further replacements or actions.

003382 HL-2203- E-3